Caenorhabditis elegans is a powerful model system for genetics and developmental biology, and for identifying biochemical targets to develop drugs active against parasitic nematodes. Eukaryotes, including nematodes and humans, share many similar metabolic pathways, which makes specific targeting challenging. Our recent studies suggest that C. elegans and other nematodes, unlike other animals, may use a plant-like pathway as the primary biosynthetic route to the major phospholipid component phosphatidylcholine. In this metabolic pathway, a pair of phosphoethanolamine methyltransferases (PMT) catalyze the sequential methylation of phosphoethanolamine to phosphocholine, which can then be incorporated into phosphatidylcholine. Importantly, both of the PMT are required for normal growth and development of C. elegans, as RNAi knockout of their expression leads to severe developmental phenotypes including arrested growth and death. This suggests that inhibition of PMT activity may be a possible strategy for controlling nematode growth. Because the PMT are not found in mammals and are highly conserved across multiple parasitic nematodes and protozoans, these enzymes are promising targets for inhibitor development; however, very little is known about how the PMT function at the molecular level. This proposal aims to explore and characterize this new metabolic pathway in C. elegans as a possible target for the development of anti-parasitic compounds. The experiments outlined in this proposal aim to address two basic and unanswered questions - what is the molecular and chemical basis for phosphobase methylation and what is the biological role of this critical metabolic pathway in C. elegans? The planned research sets out to understand the molecular basis for how the PMT function by determining the X-ray crystal structures of these enzymes and by analyzing the kinetic and thermodynamic features that define catalysis and phosphobase substrate specificity (Aims 1 and 2). To complement in vitro studies of the PMT, we will also test the metabolic contribution of these proteins to phosphatidylcholine synthesis and determine their expression patterns (Aim 3). These in vivo experiments will expand our understanding of the essential function these proteins play in the growth and development of nematodes. Because the PMT are highly conserved across nematode parasites of humans, animals, and plants, as well as in protozoan parasites, understanding how these enzymes function and identifying inhibitors targeting them will contribute to developing new anti-parasitic compounds of potential medical, veterinary, and agricultural value.